Explorer

It'll probably hook a kid with the slapstick title character and it'll take a while for them to realize Penny is the actual protagonist and hero. Then if they like there's always the 2015 show that, I believe, is also on Netflix, though I feel like they kinda dumbed down Penny in that one...

Speaking of that official channel, it's run by WildBrain, which is a branch of DHX Media that handles their web presence and they have TONS of channels with free content. Just from the Inspector Gadget channel I discovered 'Rev & Roll' which seems like a cute show for a 4-5 years old and has two girls in what seems like their 5 main characters.

A Wicked Kendragon

It was four hours old when I posted. My initial reaction was that you had Ulfgeir on ignore for some reason, but now you also copied what he said about Inspector Gadget in that very post, so now I really don't know what to think.

Anyway, yeah Carmen Sandiego! Saw the first two episodes and it was great... but I'm not sure it fits a 4 years old.

It has educational elements just like all the other incarnations of the show. On top of that, and unlike the previous versions, the new one has a straight hero in the leading role (where many of the previous ones could be said to have featured an anti-hero type). If you saw the first two episodes, then you also saw the clever swap that they do from old to new.

Explorer

It was four hours old when I posted. My initial reaction was that you had Ulfgeir on ignore for some reason, but now you also copied what he said about Inspector Gadget in that very post, so now I really don't know what to think.

Archivist

I will second She-Ra and Hilda. Also True and the Rainbow Kingdom. My daughter is 4 and loves all of these shows. Also Steven Universe; the main character is a boy but it's got some amazing female characters and Steven himself is hardly a typical "boy" hero (his main super power, other than the shield anyway, is feelings). There is a lot of nuance that I think gets lost on a younger audience, though.